The present invention relates to magnetic cores and deflection yokes having adjusting coils, such as, convergence coils wound around the cores.
Deflection yokes are assemblies of electromagnets placed around the neck of an electron-beam tube to produce a magnetic field for deflection of electron beams. Deflection yokes are provided with horizontal and vertical deflection coils for deflection of electron beams, and convergence coils for adjusting convergence of electron beams.
Convergence coils are made up of bobbins wound around which are coils that are connected to horizontal or vertical deflection coils. The bobbin has a magnetic core screwed thereinto. The core is rotated to vary the inductance of the coils wound around the bobbin to adjust the current flowing through the horizontal or vertical coils. The magnetic field generated by the horizontal or vertical coils are varied to adjust convergence of electron beams or cancel misconvergence on screen of braun tubes.
The core screwed into the bobbin is made of a baked magnetic body formed with a thread. The thread is cut on the baked body by a thread cutter. The cutter is provided with a roller and a thread cutting whetstone arranged as parallel to each other. The baked body is sent between the roller and the whetstone while the roller and whetstone are rotating to cut a thread on the baked body.
The inventors have found that the diameter of one end of the baked body, the core, is different from that of the other end when the thread cutting is completed. For example, a core of about 15 mm-long formed with a thread has one end from which the core is sent to the thread cutter and the other end, the diameter of the former end being larger than that of the latter by about 0.01 to 0.03 mm.
Screwing the cores having different diameters at both ends into bobbins causes differences in rotational torque. In fact, screwing cores from one end having a smaller diameter produces larger rotational torque than that produced when the cores are inserted into bobbins from the other end having larger diameters.
The difference in rotational torque lowers convergence adjustment efficiency. Because the rotational torque is varied for respective cores; cores would be broken when the rotational torque is too large, and cores would not be fixed in bobbins or would be moved by any accidental external shock given even after they are fixed when the rotational torque is too small. Furthermore, an effective rotational torque is not produced only by adjusting the height of protrusions that are generally formed inside the bobbins for torque adjustment. The number of times to screw the cores forwards and backwards in the bobbins thus must be changed for each core.
A purpose of the present invention is to provide a deflection yoke having an adjusting coil for which a variation of the rotational torque can be restricted when a magnetic core is inserted into a bobbin of the adjusting coil.
Another purpose of the present invention is to provide a method of producing a magnetic core that can be inserted into a bobbin from always the same end of the core.
The present invention provides a deflection yoke that includes a bobbin and an adjusting coil. The bobbin has a cavity formed in the longitudinal direction of the bobbin. The adjusting coil has a magnetic core on which a thread is cut, the core being inserted into the cavity and being slidable in the longitudinal direction of the bobbin, the core having a marker formed on only one of ends of the core in the longitudinal direction, the core having been inserted into the cavity from the one end formed with the marker or the other end.
Furthermore, the present invention provides a method of producing a core. A marker is formed on only one of ends of the core in the longitudinal direction thereof. And, a thread is cut on the core from the one end formed with the marker or from the other end.
Furthermore, the present invention provides a method of producing a core. A thread is cut on the core. And, a marker is formed on only one of ends of the core in the longitudinal direction thereof.